Drawing
Dimensions

Writing
Dimensions with Different Units

Setting
Dimension Styles

Adding
Hatch Patterns to Drawings

Drawing
Symbols

Drawing
Arrows

The
Artistic Side of CADD

AutoCAD,
MicroStation and Cadkey Terms

About
this ChapterThis
chapter focuses on the two-dimensional drawing functions of
CADD. It describes in detail how to draw each element of a
drawing. You will learn the unique characteristics of different
drawing elements that make them suitable for specific drawing
tasks.

In
this chapter you will learn the following:

How
to create line types such as dotted lines, dashed lines,
multi-lines and splines.

How
to draw arcs, circles and ellipses.

How
to write text and dimensions with different styles and
how to control various aspects associated with them such
as size, fonts and units.

How
to make drawings presentable using drawing annotations
such as symbols, arrows, borders and hatching patterns.

Key
Terms in this Chapter

Term

Description

Associative
dimensions

A
mode of dimensioning that automatically updates dimension
values when the dimension size is changed.

Benchmark

A
reference point from where all distances are measured.

Spline

A
flexible curve that can be drawn to fit any shape.

Hatch
patterns

Ready-made
patterns that can be added to a specified area in a drawing.

Justification

The
alignment of text strings in a specific direction such as
to the right, left, or center.

Polyline

A
string of lines that may contain a number of line segments
connected together.

Tangent

A
point on a circle that forms 90° angle between the center
point of the circle and another point outside the circle.

There
are a number of line types available in CADD that can be used
to enhance drawings. There are continuous lines, dotted lines,
center lines, construction lines, etc. Fig. 3.1 shows some
examples of common line types used in architectural and engineering
drawings.

CADD
enables you to follow both geometrical and engineering drawing
standards. You can use line types to represent different
annotations in a drawing. For example, an engineer can use
line types to differentiate between engineering services
in a building plan. One line type can be used to show power
supply lines, while the others to show telephone lines,
water supply lines and plumbing lines.

CADD
is preset to draw continuous lines. When you enter the line
command and indicate a starting point and end point, a continuous
line is drawn. If you want to draw with another line type,
you need to set that line type as the current line type.
Thereafter, all the lines are drawn with the newly selected
line type.

Note:

You
can change the line type of an existing line using CADD's
editfunctions. Some people prefer to first draw everything
with one line typeand later change line types as needed;
others prefer to draw everythingwith the right line type
the first time.

Drawing
Multiple Parallel Lines

CADD
allows you draw parallel lines simultaneously just by indicating
astarting point and an end point. These lines can be used
to draw somethingwith heavy lines or double lines. For example,
they can be used to draw thewalls of a building plan, roads
of a site map, or for any otherpresentation that requires
parallel lines.

Most
programs allow you to define a style for multiple parallel
lines. Youcan specify how many parallel lines you need,
at what distance and if theyare to be filled with a pattern
or solid fill.

A
number of add-on programs use multiple lines to represent
specificdrawing features. For example, an architectural
program has a specialfunction called "wall'. When you use
this option, it automatically drawsparallel lines representing
walls of specified style and thickness.

Note:

Multiple
lines are a unified entity. Even though double lines are
drawn,they are treated as one line. You cannot erase or
edit one line separately.However, there are functions available
that can break the entities apart.

Drawing
Flexible Curves

CADD
allows you to draw flexible curves (often called splines)
that can beused to draw almost any shape. They can be used
to create the smooth curvesof a sculpture, contours of a landscape
plan or roads and boundaries of amap.

To
draw a flexible curve, you need to indicate the points through
which thecurve will pass. A uniform curve is drawn passing
through the indicatedpoints. The sharpness of the curves,
the roughness of the lines and thethickness can be controlled
through the use of related commands.

Note:

The
computer needs a lot of memory to draw flexible curves;
they should beused only when necessary.

Drawing
Arcs and Circles

CADD
provides many ways to draw arcs and circles. There are a number
ofadvanced techniques available for drawing arcs and circles,
which cansimplify many geometrical drawing problems. You can
draw an arc byspecifying circumference and radius, radius
and rotation angle, chordlength and radius, etc.

Arcs
are drawn so accurately that a number of engineering problems
can besolved graphically rather than mathematically. Suppose
you need to measurethe circumference of an arc, just select
that arc and the exact value isdisplayed.

The
following are basic methods for drawing arcs and circles:(These
are essentially the same methods you learn in a geometry
class.However, when drawing with CADD the approach is a
little different.)

Center
point and radius

3
points

Angle
and radius

2
points

2
tangents and a point

3
tangents

Note:
The above topics are described in detail in CADD PRIMER.

Drawing
Ellipses and Elliptical Arcs

Ellipses
are much easier to draw with CADD than on a drawing board.
On adrawing board, you need to find the right size template
or draw a series ofarcs individually to draw an ellipse. With
CADD, all you need to do isspecify the size of the ellipse.

The
following are two basic methods for drawing ellipses:

Length
and width

Axis
and rotation angle

Length
and Width

An
ellipse has two axes: a major axis and a minor axis (Fig.
3.6). Themajor axis determines the length of the ellipse
and the minor axisdetermines the width.

To
draw an ellipse you need to specify length and width, i.e.,
major axisand minor axis. You can enter the values numerically
or by indicatingpoints in the drawing area. When you need
to draw an ellipse rotated at anangle, you can indicate
the axis rotated at an angle. (Fig. 3.6.) To drawan elliptical
arc, enter the starting point and the end point of theellipse
in addition to indicating the axes.

Axis
and Rotation Angle

When
a circle is viewed at an angle, it takes on an elliptical
shape. CADDuses the same principle to draw an ellipse. It
takes a circle and rotatesit into 3D space around one of
the axes. As a result, the width of thecircle is reduced
and an ellipse is drawn (Fig. 3.7).

To
draw an ellipse, you need to specify the length of the ellipse
(majoraxis) and the rotation angle. The computer automatically
calculates itswidth and draws an ellipse.

Note:

In
advanced engineering systems, a number of additional methods
for drawingelliptical arcs are available. These methods
enable you to draw a varietyof elliptical shapes, including
a parabola and a hyperbola.

Adding
Text to Drawings

CADD
allows you to add fine lettering to your drawings. You can
use text towrite notes, specifications and to describe the
components of a drawing.Text created with CADD is neat, stylish
and can be easily edited. Typingskills are helpful if you
intend to write a lot of text.

Writing
text with CADD is as simple as typing it on the keyboard.
You canlocate it anywhere on the drawing, write it as big
or as small as you likeand choose from a number of available
fonts.

Note:

When
large amounts of text are added to drawings, it slows down
the screendisplays. Many programs provide options to temporarily
turn off text or todisplay text outlines only. This feature
helps save computer memory andspeeds up the display of screen
images. The text can be turned back onwhenever needed.

The
following are the basic factors that control the appearance
of text:(The
exact terms and procedures used vary from one program to
another.)

Text
height

Height
to width ratio and inclination of letters

Special
effects

Alignment
of text (justification)

Text
fonts

Note:
The above topics are described in detail in CADD PRIMER.

Important
Tips:

The
fonts used in a drawing must be supported by the printer
or plotterused for printing the drawing. You may want to
do a test plot before usingspecific fonts in a drawing.

When
you need to send drawings electronically, make sure to
include anyspecial fonts you might have used in the drawing.
Otherwise, the recipientmay not be able to open the drawings.

You
can change the appearance of text using the editing functions
ofCADD. You can change the height, width, inclination,
rotation, spacing,fonts, justification, etc., as needed.

Note:
CADD PRIMER is illustrated with more than 100 diagrams.
The above diagram is an example from CADD PRIMER showing
line types used in CAD.